Along with an increase in demand of data communication service in recent years, the introduction of a longer-distance, larger-volume high-density wavelength multiplexing optical fiber communication system with higher reliability is being promoted. On such a background, higher performance of an optical communication system that uses optical fibers is being demanded. As part thereof, the adoption of a digital coherent reception system in which a digital processing technique is introduced to an optical receiver is being promoted.
In the digital coherent reception system, it is possible to correct, by digital processing, linear degradation of an optical waveform due to optical fiber transmission, and compensate transmission characteristic degradation due to a wavelength dispersion characteristic of an optical fiber as a transmission channel. However, due to the wavelength dispersion, an optical signal waveform collapses and expands in an amplitude direction, so in a digital conversion, a dynamic range for an analog/digital conversion becomes a problem.
As a communication system that takes the wavelength dispersion characteristic into consideration, Patent Literature 1 discloses a method of changing a dynamic range at a time when an analog electric signal is converted into a digital electric signal by monitoring wavelength dispersion.